The industries’ push for alternative feed ingredients and current prices of aquafeed has led nutritionists and researchers to focus towards optimizing feed efficiency. Evaluating lipids and optimizing alternative sources for the use of fish oil revealed that l ipids are involved not only in growth, but also in health and development. Vegetable oils, like s oybean oil , are commonly applied in current Nile Tilapia feeds as alternative. However, this inclusion has led to decreased growth performance and health concerns including decreased anti-oxidant status. Nutritional emulsifiers traditionally increase the surface area of fat globules by breaking them down to micelles allowing for improved lipid digestion. Although there is sufficient evidence of improved performance and immunity with proper application of nutritional emulsifiers in terrestrial livestock species, the application in aqua remains limited.
The objective of this study was to investigate effects of dietary lipid levels using a commercial nutritional emulsifier (NE; Excential Energy Plus by Orffa additives B.V., the Netherlands ) on the growth, feed utilization, immune response and lipid metabolism of juvenile Nile Tilapia. A 5x2 factorial design was implemented with lipid supplement ( Soybean oil at 0, 15, 30, 45 and 60 g/kg) and NE supplementation (with or without NE at 0.35 g/kg), creating 10 iso-energetic diets. All dietary treatments were fed in triplicate, 30 fish per replicate (average initial weight of 8.06 g) were randomly stocked in one of the 30 cages and were on feeding treatment for 8 weeks.
Results showed that fish fed diets with NE for 8 weeks had significantly improved weight gain compared with fish fed diets without NE (p<0.05) , especially for the diet with the lowest lipid content (234% increase) (Table 1). The same results have been observed for the FCR and PER (p<0.05) (Table 1).
After 8 weeks, six fish per treatment were randomly chosen to have non-specific immune parameters and antioxidant activities measured. Increasing dietary lipid levels significantly decreased anti-oxidant status and increased liver malondialdehyde , but significantly improved when NE was supplemented (p<0.05).
Lipid supplementation was shown to have little effect on the fillet yield, whilst when NE was supplemented in the diet, the fillet content of the fish significantly increased, especially in fish fed the low fat diet (p<0.05) (Figure 1).
In summary, dietary NE supplementation has a positive effect on feed digestion and absorption, resulting in improved fish growth, performance, anti-oxidant status and fillet yield. NE supplementation is particularly effective when it is added to diets with low crude fat diets , giving feed formulators the opportunity to decrease fat inclusion in the diet.